(Adapted from the applicant's abstract) The clinical core of this SCOR will direct the management of clinical studies of the pathogenesis and treatment of acute respiratory failure in the term and pre-term infant. The core will identify appropriate patients for study, be responsible for informed consent and management of the patient as pertains to the conduct of the study. The core will handle collection of and distribution to the basic science investigators of clinical samples. Central data collection and analysis facilities along with dedicated biostatistical consultation will be provided. Arrangements with collaborators to facilitate and augment the clinical studies will be the responsibility of the core. The most important goal of this core is to facilitate the smooth transition of results of bench research of the basic science investigators to studies and/or therapeutic trials in the nursery. The core will collaborate on these investigators on the design of clinical projects and will work with the Institutional Review board to assure proper protection for the infants participating in these studies. Acute respiratory failure with associated pulmonary hypertension is a major cause of morbidity and mortality in both term and pre-term infants. In the pre-term infant, the use of surfactant replacement therapy has decreased mortality from respiratory disease. However, some infants fail to respond or respond poorly to the administration of exogenous surfactant. Associated pulmonary hypertension contributes to the severity of illness in these infants. One focus of the clinical core will be to examine the hypothesis that severe respiratory failure in the pre-mature infant is in part related to vascular abnormalities and pulmonary hypertension. The pathogenesis of the condition will be studies using echocardiography and measurement of mediators of vascular regulation and oxidant injury. The study of pathogenesis will take place within the context of a placebo controlled study of the safety and efficacy of the specific pulmonary vasodilator, inhaled nitric oxide. The core will also expand upon previous success upon previous success with new management strategies in the term infant with respiratory failure. Inhaled nitric oxide has been shown to be a useful therapy in many of these infants. However, some infants respond poorly or only partially to this therapy. The focus of the core in these infants will be to understand the pathogenesis of a poor response and the development of adjunctive therapy to augment the response to inhaled nitric oxide in this group of infants. Finally, the core will run a follow up program for all infants treated in therapeutic trials treating respiratory failure in pre-term and term infants to assess the safety of the new therapies in the context of neurodevelopmental and cardiopulmonary outcomes.